Create Java Phone Book Application Using Structure Array

In this example, you create a Java^® package that calls a MATLAB^® function to modify a structure array and implement a phone book application.

Files

MATLAB Function	makephone.m
MATLAB Function Location	matlabroot\toolbox\javabuilder\Examples\PhoneExample\PhoneDemoComp\
Java Code Location	matlabroot\toolbox\javabuilder\Examples\PhoneExample\PhoneDemoJavaApp\getphone.java

Procedure

1. Copy the PhoneExample folder that ships with MATLAB to your work folder:

   copyfile(fullfile(matlabroot,'toolbox','javabuilder','Examples','PhoneExample'),'PhoneExample')

   At the MATLAB command prompt, navigate to the new PhoneExample\PhoneDemoComp subfolder in your work folder.

2. Examine the makephone.m function.

   function book = makephone(friends)
   book = friends;
   for i = 1:numel(friends)
       numberStr = num2str(book(i).phone);
       book(i).external = ['(508) 555-' numberStr];
   end

   The function takes a structure array as an input, modifies it, and supplies the modified array as an output.

3. Build the Java package with the Library Compiler app or compiler.build.javaPackage using the following information:

   Field	Value
   Library Name	phonebookdemo
   Class Name	phonebook
   File to Compile	makephone.m

   For example, if you are using compiler.build.javaPackage, type:

   buildResults = compiler.build.javaPackage('makephone.m', ...
   'PackageName','phonebookdemo', ...
   'ClassName','phonebook');

   For more details, see the instructions in Generate Java Package and Build Java Application.

4. Write source code for an application that accesses the MATLAB functions.

   The sample application for this example is in PhoneExample\PhoneDemoJavaApp\getphone.java.

    getphone.java

   /* Necessary package imports */
   import com.mathworks.toolbox.javabuilder.*;
   
   import phonebookdemo.*;
   
   /*
    * getphone class demonstrates the use of the MWStructArray class
    */
   class getphone
   {
       public static void main(String[] args)
       {
           phonebook thePhonebook = null;     /* Stores magic class instance */
           MWStructArray friends = null; /* Sample input data */
           Object[] result = null;    /* Stores the result */
           MWStructArray book = null; /* Output data extracted from result */
           
           try
           {
               /* Create new magic object */
               thePhonebook = new phonebook();
               
               /* Create an MWStructArray with two fields */
               String[] myFieldNames = {"name", "phone"};
               friends = new MWStructArray(2,2,myFieldNames);
               
               /* Populate struct with some sample data --- friends and phone numbers */
               friends.set("name",1,new MWCharArray("Jordan Robert"));
               friends.set("phone",1,3386);
               friends.set("name",2,new MWCharArray("Mary Smith"));
               friends.set("phone",2,3912);
               friends.set("name",3,new MWCharArray("Stacy Flora"));
               friends.set("phone",3,3238);
               friends.set("name",4,new MWCharArray("Harry Alpert"));
               friends.set("phone",4,3077);
               
               /* Show some of the sample data */
               System.out.println("Friends: ");
               System.out.println(friends.toString());
               
               /* Pass it to a MATLAB function that determines external phone number */
               result = thePhonebook.makephone(1, friends);
               book = (MWStructArray)result[0];
               System.out.println("Result: ");
               System.out.println(book.toString());
               
               /* Extract some data from the returned structure */
               System.out.println("Result record 2:");
               System.out.println(book.getField("name",2));
               System.out.println(book.getField("phone",2));
               System.out.println(book.getField("external",2));
               
               /* Print the entire result structure using the helper function below */
               System.out.println("");
               System.out.println("Entire structure:");
               dispStruct(book);
           }
           catch (Exception e)
           {
               System.out.println("Exception: " + e.toString());
           }
           
           finally
           {
               /* Free native resources */
               MWArray.disposeArray(result);
               MWArray.disposeArray(friends);
               MWArray.disposeArray(book);
               if (thePhonebook != null)
                   thePhonebook.dispose();
           }
       }
       
       public static void dispStruct(MWStructArray arr) {
       	System.out.println("Number of Elements: " + arr.numberOfElements());
       	//int numDims = arr.numberOfDimensions();
       	int[] dims = arr.getDimensions();
       	System.out.print("Dimensions: " + dims[0]);
       	for (int i = 1; i < dims.length; i++)
       	{
       		System.out.print("-by-" + dims[i]);
       	}
       	System.out.println("");
       	System.out.println("Number of Fields: " + arr.numberOfFields());
       	System.out.println("Standard MATLAB view:");
       	System.out.println(arr.toString());
       	System.out.println("Walking structure:");
           java.lang.String[] fieldNames = arr.fieldNames();
           for (int element = 1; element <= arr.numberOfElements(); element++) {
               System.out.println("Element " + element);
               for (int field = 0; field < arr.numberOfFields(); field++) {
               	MWArray fieldVal = arr.getField(fieldNames[field], element);
               	/* Recursively print substructures, give string display of other classes */
               	if (fieldVal instanceof MWStructArray)
               	{
                   	System.out.println("   " + fieldNames[field] + ": nested structure:");
                   	System.out.println("+++ Begin of \"" + 
                                                 fieldNames[field] + "\" nested structure");
               		dispStruct((MWStructArray)fieldVal);
                   	System.out.println("+++ End of \"" + fieldNames[field] +
                                                                     "\" nested structure");
               	} else {
                   	System.out.print("   " + fieldNames[field] + ": ");
                       System.out.println(fieldVal.toString());          		
               	}
               }
           }
       }
   }

   The program does the following:

   • Creates a structure array, using MWStructArray to represent the example phonebook data.

   • Instantiates the plotter class as thePhonebook object:

     thePhonebook = new phonebook();

   • Calls the makephone method to create a modified copy of the structure by adding an additional field:

     result = thePhonebook.makephone(1, friends);

   • Uses a try-catch block to catch and handle any exceptions.

5. In MATLAB, navigate to the PhoneExample\PhoneDemoJavaApp folder.

6. Copy the generated phonebookdemo.jar package into this folder.

   • If you used compiler.build.javaPackage, type:

     copyfile(fullfile('..','PhoneDemoComp','phonebookdemojavaPackage','phonebookdemo.jar'))

   • If you used the Library Compiler, type:

     copyfile(fullfile('..','PhoneDemoComp','phonebookdemo','for_testing','phonebookdemo.jar'))

7. In a command prompt window, cd to thePhoneDemoJavaApp folder.

8. Compile the getphone application using javac.

   • On Windows^®, type:

     javac -classpath "matlabroot\toolbox\javabuilder\jar\javabuilder.jar";.\phonebookdemo.jar getphone.java

   • On UNIX^®, type:

     javac -classpath "matlabroot/toolbox/javabuilder/jar/javabuilder.jar":./phonebookdemo.jar getphone.java

   Replace matlabroot with the path to your MATLAB or MATLAB Runtime installation folder. For example, on Linux^®, the path may be /usr/local/MATLAB/R2024b.

9. Run the getphone application.

   • On Windows, type:

     java -classpath .;"matlabroot\toolbox\javabuilder\jar\javabuilder.jar";.\phonebookdemo.jar getphone

   • On UNIX, type:

     java -classpath .:"matlabroot/toolbox/javabuilder/jar/javabuilder.jar":./phonebookdemo.jar getphone

     Note

     If you are running the application on the Mac 64-bit platform, you must add the -d64 flag in the Java command.

   The getphone program displays the following output:

   Friends: 
   2x2 struct array with fields:
       name
       phone
   Result: 
   2x2 struct array with fields:
       name
       phone
       external
   Result record 2:
   Mary Smith
   3912
   [phone]
   
   Entire structure:
   Number of Elements: 4
   Dimensions: 2-by-2
   Number of Fields: 3
   Standard MATLAB view:
   2x2 struct array with fields:
       name
       phone
       external
   Walking structure:
   Element 1
      name: Jordan Robert
      phone: 3386
      external: [phone]
   Element 2
      name: Mary Smith
      phone: 3912
      external: [phone]
   Element 3
      name: Stacy Flora
      phone: 3238
      external: [phone]
   Element 4
      name: Harry Alpert
      phone: 3077
      external: [phone]